Luxury-home swappers say mansion exchanges save them money and give them the experience of staying in otherwise inaccessible homes.

Gaelle Deschamps struck out for Vietnam from France in August with her family of five in tow. Upon arrival, they spent two weeks at a private beachfront villa staffed by cooks, housekeepers, a driver and personal concierge. The cost: $495 a week.

The bargain stems from the fact that she and her husband, Marc, open the doors of their 18th-century, 10,700-square-foot château in France's Loire Valley to similarly well-heeled...